[RPG] Is Bleed worth optimizing

I don't think so.

A few things up front.

There are several important issues to address regarding Bleed effects.

Rules as intended

James Jacobs (Creative Director of Paizo) has clarified on the "Ask JJ" thread that the RAI about stopping bleed damage is (emphasis mine):

Anything that heals hit point damage stops bleed damage.

Not only does that match the rules as intended, it's simple to remember. And there's NO GOOD REASON why cure light wounds should be able to stop bleed damage when a potion of cure light wounds (also not a spell) won't do the same thing. Or fast healing or channel energy or anything else.

If it heals hp damage, it stops all bleed effects.

Then again, he also states that drinking a potion does not "apply" the spell to the drinker, so his rules interpretations are not universally accepted.

Nevertheless, JJ's RAI increases the amount of creatures immune to bleed damage drastically, including everything that has Regeneration or Fast Healing.

Stacking Bleed

Bleed damage does not normally stack with other bleed damage. From the bleed condition:

[...] Bleed effects do not stack with each other unless they deal different kinds of damage. When two or more bleed effects deal the same kind of damage, take the worse effect. [...]

Because of this strict non-stacking rule, I believe Bleeding Critical to be the only worthwhile source of bleed damage, since:

The effects of this feat stack.

This supersedes non-stacking of bleeding in general, which means that you can potentially stack this indefinitely. Because of this, I believe it to be the only Bleed ability that's worth considering for serious damage.

Immunity count

The following data was gathered by running a Python script that analyzes the Monster database on d20pfsrd.com.

Creatures types and subtypes immune to bleed

Creature Types and Subtypes generally immune to bleed damage, with average CR^*:

• Undead: 250 Creatures, CR 6.88±4.8
• Construct: 167 Creatures, CR 8.11±4.98
• Elemental: 156 Creatures, CR 7.84±5.33
• Kami: 11 Creatures, CR 10.33±6.48
• Behemoth: 3 Creatures, CR 20.0±2.0

^{*Due to technical reasons, "CR +1" templates are counted as "CR 1" creatures}

Undead, Construct and Elemental are pretty dominant creature types. (Interestingly, incorporeal creatures seem to bleed just fine)

If you add the immunities via RAI, you can include many high level outsiders as well. In total, the numbers are as follows:

• Fast Healing: 196 Creatures, CR 11.34±6.96:
• Regeneration: 196 Creatures, CR 15.6±7.98:

These may overlap with the creature types above, though.

Critical hit immunes

Bleeding Critical requires you to crit, which means you can add

• Ooze: 72 Creatures, CR 6.92±4.85
• Swarm: 67 Creatures, CR 4.7±3.43
• Aeon: 5 Creatures, CR 11.4±7.13:5

to the list of immunes due to immunity to critical hits. Again, these may overlap, particularly in case of swarms (I do remember construct swarms being a thing)

Adding the numbers

In total, there are 964 creatures (this number should not include doubles) that are immune to Bleed, have Regeneration or Fast Healing, or are immune to criticals. The average CR of these creatures is 9.24±6.78.

Doing it anyway

If you want to build for bleed optimization, there's actually not much you can do, since you only need a single source of Bleed (which is Bleeding Critical). That said, optimizing for Bleed is just taking Bleeding Critical on top of a critical hit focused build.

Off the top of my head I'd suggest dual-kukri wielding Two-Weapon Warrior Fighter, as this is quite feat intensive, and getting a whole bunch of attacks helps. Take Improved Critical at 8th, Critical Focus at 9th and Bleeding Critical at 11th.

Since you are there anyway, I'd pick up Critical Mastery at 14th, and alternative critical feats to keep your game up whenever your enemy refuses to bleed.

Note that retraining allows you to use your low-level feat slots for high prereq feats as well.